I've made a fair bit of progress since last time:

Let's start with the tender.

Believe it or not, I've managed to re-use the B12 tender... I had to saw the chassis into three, and then use 2mm square plastic strip to lengthen it and also give the appearance of the tank being lower than it actually is. The tank itself was sawn in half and the fake coal sawn away (along with all of the top of the tank). I was then able to insert a 7mm length of plastic sheet between the two halves and then overlay 0.5mm sheet over the tank sides to commence th transformation. I've taken this a stage or two further and added more 2mm square strip, around the top of the tank sides, so that eventually I can run some milliput along the tank top to get the curved outer edge to the tender.

Moving forward onto the lcoomotive proper, One thing I have done is use 0.5mm sheet to give a homogenous edge to the running plate. Plainly it still needs work but already it looks better for losing the 'three-penny bit' effect along the edge of the running plate. I've used 0.64mm plastic rod for the steampipe along the boiler, but personally I think this looks too small- short of replacing it (a real chore now that the only model shop in Birmingham that I knew to stock 1mm rod has closed down), I'm not sure what I can do about this. Boiler bands have been added from paper strips.

It looks much better just for being painted up in primer- even if this does bring out all of the gaps and rough edges- but then again that's why I've painted it!

Next step(s) clearly will be to get the rougher bits sanded out and smoothed down.